The present invention relates, in general, to generating optical images and, more particularly, to generating stereoscopic images.
Typically, work pieces such as semiconductor devices are visually inspected to insure that they meet design specifications for parameters such as lead coplanarity, lead length, lead straightness, mark inspection, surface inspection, lead pitch, etc. A common approach for performing the visual inspection includes using a machine vision system to form an image of the lead in a camera. Two common techniques for providing light in machine vision systems are front lighting and back lighting techniques. A limitation of the front lighting technique is that metal leads are reflective and can cast hot spots, cold spots, or other distortions to the camera, which lead to inaccurate results being generated by the vision computer. The image of the lead formed in the camera using either front lighting or back lighting technique is usually a two dimensional image. The accurate measurement of lead parameters such as position, coplanarity, package standoff are difficult with the two dimensional image.
A laser triangulation scanning technology can be used to generate a three dimensional image of the lead, thereby facilitating the accurate measurement of lead parameters. Alternatively, two pictures of the lead having different directions of views can be formed. Each picture is a two dimensional image of the lead. A three dimensional image of the lead can be reconstructed from the two pictures. Both of these approaches are complicated and time inefficient. They also require apparatuses that are expensive. Further, the apparatuses are often too bulky to be incorporated into existing equipment such as, for example, part handlers, vision inspection systems, etc.
Accordingly, it would be advantageous to have a method and an apparatus for generating a stereoscopic image. It is desirable for the method to be simple and time efficient. It is also desirable for the apparatus to be inexpensive and small. It would be of further advantage for the apparatus to be compatible with existing equipment and inspection process.